Densification of formed composite parts

ABSTRACT

Methods and apparatuses for combining raw fibrous and binding materials in single mixing step (Step S 3 ), followed by consolidation (Step S 5 ) to greatly shorten overall cycle time to finished fiber-reinforced composite part. Chopped fibrous materials and binder materials are deposited sequentially onto belt conveyor (Step S 2 ) so that materials are successively layered on top of one another in predetermined ratio and subsequently mixed (Step S 3 ) to achieve uniform dispersion throughout. Mixed materials are deposited into rotating mold (Step S 4 ), which further ensures uniform dispersion of fibrous and binder materials. Impregnation of fibrous materials with the binder material occurs in situ as uniformly mixed materials are heated and subsequently compacted in mold (Step S 5 ) to obtain desired shape of fiber-reinforced composite part. Rotation device including: turntable for rotating mold; and actuator for supporting turntable and providing reciprocating motion to mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/315,464,filed Dec. 10, 2002. Ser. No. 10/315,464 is in turn a divisional ofapplication Ser. No. 09/527,322, filed Mar. 16, 2000, now U.S. Pat. No.6,521,152. Benefit of the filing dates of these two parent applicationsis claimed under 35 U.S.C. § 120. The entire disclosure of each of theparent applications is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for formingfiber reinforced composite parts.

BACKGROUND OF INVENTION

Fiber-reinforced composite structures, such as carbon-carbon compositesfor example, are widely used as friction materials for heavy-duty brakesin automobiles, trucks, and aircraft. This is because they exhibit highthermal conductivity, large heat capacity, and excellent friction andwear characteristics and thus can provide excellent performance.

However, past manufacturing processes for producing thesefiber-reinforced composite structures were often lengthy undertakings,requiring months to fabricate a single part. In one example, a typicalfiber-reinforced composite part such as a preform was prepared by anon-woven process that involved needle-punching layers of carbon fibers,a slow, time-consuming process. When two or more layers of fibers areneedle punched together by metal needles having barbs on one end, thebarbs commingle fibers from a particular layer into successive layers.The commingled fibers essentially stitch the layers of fabric together.This non-woven technology achieved preform densities on the order ofabout 0.5 g/cc. To obtain a final composite part, the preform wassubsequently infiltrated with a matrix binder material via a chemicalvapor deposition (“CVD”) or chemical vapor infiltration (“CVI”) process,for example. CVD and CVI are used interchangeably for the purposes ofthe present application.

In another process, a preform was prepared by building up successivelayers of pre-impregnated carbon fiber fabric. Tows (the term “tow” isused hereinafter to refer to a strand of continuous filaments) of carbonfiber were woven into a two-dimensional weave, and thereupon dipped intoa liquid batch to impregnate the weave with a liquid resin. Theresin-impregnated weave was then pulled between rollers to form a sheetof pre-impregnated carbon-fiber fabric. A plurality of desired shapeswere then cut out of the sheet material and stacked within a mold, andsubsequently cured using heat and pressure to obtain the desiredcomposite part. However, the procedure for impregnating a binder intothe pores of the fibrous material was often repeated many times, whichcumulatively decreased porosity of the resultant composite. For thisreason, it often took a term of several months to obtain a finalproduct, causing the product to be extremely expensive. Further, muchmaterial was wasted in order to obtain the final product.

Several processes have been developed in order to reduce overallprocessing time needed to manufacture a fiber reinforced composite part.One process, a “random-fiber process”, uses entirely tow material.Somewhat similar to the pre-impregnating method described above, in therandom-fiber process a continuous tow of fiber is dipped through a resinbath and then chopped up, whereupon the resin coated chopped fibers areplaced into a mold for curing by heat and pressure. However, the stepsof dipping the continuous tow are performed separately from the moldingand curing required to create the composite part, thereby extending the“process cycle” of manufacturing the composite part.

Another method involves a molding compound process whereby choppedfibrous material are mixed with a resin so as to form a continuous sheetof mixed material. A plurality of desired shapes are then cut out of thesheet material and stacked within a mold, and subsequently cured usingheat and pressure to obtain the desired composite part. Again, thisprocess requires extensive time and wastes material in order to obtainthe final product.

A further process developed to shorten the manufacturing time involvesusing a liquid slurry to mix the fibrous material with a resin powder,as illustrated in U.S. Pat. No. 5,744,075 to Klett et al. However, thefibrous material needs to be chopped into small pieces (on the order of¼ to ½ inch (about 0.6-1.3 cm)) so as to attain a uniform mix with theresin powder in the slurry. Thus, longer chopped fibers (1-1½ inches(about 2.5-3.8 cm)) do not work well in this liquid slurry method, sincea uniform dispersion of fibrous material and resin powder in the slurrycannot be attained with the longer chopped fiber lengths. The longerfibers tended to “ball-up” during mixing with the powdered resin andduring deposition into the mold, making it difficult to obtain a uniformend product. Moreover, this “balling effect” directly contributed to the“loftiness” of the preform, a disadvantageous result of the water slurrymethod since a lofty preform was difficult to control within the mold.Additionally, an excess step of drying the preform was required (i.e.,removing the water from the preform in the heating step is requiredbefore pressing the materials in the mold into a composite part).Further, and similar to the above methods, a continuous tow of fibrousmaterial needs to be chopped before mixing the fibrous chop with theresin binder.

Recent developments have introduced a method and apparatus that combineschopped fibers and a powdered resin utilizing a dry-blending process.Such a dry-blending process and apparatus 100 is illustrated in therough schematic diagram of FIG. 1. Apparatus 100 includes a first lowerenclosure 101 connected to a second upper enclosure 102 via a neckportion 119. First enclosure 101 has an adjuster 120 connected theretowhich houses compressed air lines 121 and 124 for feeding air jets 122.Second enclosure 102 houses a screen 126, and has a funnel 132 andvacuum line 135 connected thereto.

In FIG. 1, chopped tow 115 is loaded into first enclosure 101, where airjets 122 feed compressed air into the chopped tow 115 within firstenclosure 110. The compressed air fed via compressed air lines 121 andair jets 122 enters below the level of chopped tow in first enclosure101. This compressed air forces the chopped tow 115 into upper portion117 of first enclosure 101 such that the individual fibers of thechopped tow 115 are entrained in air and further broken-up(defibrillated) into smaller strands or filaments 118. Adjuster 120maintains the compressed air jets 122 at a level equal to or below thechopped tow 115 within first enclosure 101.

The broken-up fibers 118 entrained in air in the upper section 117 arethen forced through neck portion 119 into a second enclosure 102,whereby they are mixed with a powdered resin 130 fed through at funnel132 of second enclosure 102. The powder resin 130 mixes with thebroken-up fibers in a powder and fiber mixing region 140, whereupon the“mixed materials” settle at the bottom of second enclosure 102 to form alayer which constitutes the building-up of a preform 125. The mixedmaterials fall due to a vacuum 135 being applied to the bottom of secondenclosure 102 which removes the bulk of the air volume in secondenclosure 102, thereby allowing the mixed materials to fall and condenseat the bottom of second enclosure 102 on top of screen 126.

The “dry-blending” apparatus of FIG. 1 provides a medium for mixing thepowder 130 with the fibrous material (chopped tow 115) to attain auniform mixture of the binder material with the fibrous material.However, in the apparatus 100 of FIG. 1, the proportions of choppedfiber and binder material have to be first individually weighed out toobtain the proper proportions, before being loaded in enclosures 101 and102 to be mixed in mixing region 140. Further, apparatus 100 of FIG. 1is limited to a single-batch process, i.e., to make one finalfiber-reinforced composite part, the individual proportions for eachfibrous material and binder material have to be weighed and addedindividually for each preform made.

Yet a further process to shorten the manufacturing cycle time of acomposite part is illustrated in U.S. Pat. No. 5,236,639 to Sakagami etal. The objective of this process is to provide excess carbon materialto fill pores in the matrix material during subsequent curing andcarbonization steps, thus producing a carbon-carbon composite materialthat requires no repetition of production steps including any furtherdensification of the composite material. This involves mechanicallymixing a matrix carbon material and carbon fibers in proportions thatare determined on the basis of the carbonization ratio of the matrixmaterial and on the basis of the desired ratio of fibers to be containedin a resultant end product. However, such a process requires the use ofexcess carbon matrix material, a curing step under pressure afterformation of an intermediate-formed part such as a preform or mold, andalso requires subsequent carbonization and graphitization of the curedintermediate part, both under pressure, to obtain the finalfully-densified composite part. Of course, no further production stepsare required or repeated, including densification of the compositematerial. However, it is costly and time consuming to perform thecuring, carbonization and graphitization all under pressure.

Therefore, what is desired is a method and apparatus which would feed,blend, and deposit various lengths of chopped fibrous and bindermaterials into a mold of a desired final shape, wherein the raw fibrousmaterials and binder materials are combined in a single step, followedby consolidation of the materials. The resultant preform would notrequire any curing or carbonization under pressure during the follow-onheating processes to manufacture the final composite part. Such a methodand apparatus would provide fiber-reinforced composite parts withdensities that are higher than achieved with current technologies, andwould decrease overall cycle time to a finished composite part. Themethod can be used to provide an intermediate preform product that issubsequently stabilized, carbonized, optionally heat treated, densified,and final heat treated to provide a carbon-carbon composite material.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for combining rawfibrous and binding materials in a single mixing step, followed byconsolidation so as to greatly shorten the overall cycle time to afinished fiber-reinforced composite part. In the method, chopped fibers,which can include single length or multiple lengths of fibrous material,and a powdered resin binder material are combined in a continuousprocess at predetermined ratios, mixed together, and deposited into amold having the shape of the final product. Specifically, the choppedfibrous materials and binder materials are deposited sequentially onto abelt conveyor so that the materials are successively layered in apredetermined ratio, and subsequently mixed to achieve uniformdispersion throughout. The “mixed materials” are then deposited into arotating mold to further ensure uniform dispersion of fibrous and bindermaterials, wherein impregnation of the fibrous materials with the bindermaterial occurs in-situ as the uniformly mixed materials are heated inthe mold, and subsequently compacted to obtain the final desired shapeof the preform. The resultant preform requires no excess use of matrixmaterial, no curing or carbonization under pressure in the follow-onheating processes required to obtain the intermediate fiber-reinforcedcomposite part.

Objectives of the present invention will become more apparent from thedetailed description given hereinafter. However, it should be understoodthat the detailed description and specific examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawings,wherein like elements are represented by like reference numerals, whichare given by way of illustration only, and thus are not limitative ofthe present invention and wherein:

FIG. 1 illustrates a conventional dry-blending apparatus;

FIG. 2 is a schematic diagram of the equipment and major components usedin accordance with the preferred embodiment of the present invention;

FIG. 3 illustrates a device to rotate the mold in accordance with thepreferred embodiment of the present invention;

FIG. 4 illustrates general processing steps performed in accordance withthe preferred embodiment of the present invention;

FIG. 5 illustrates the feeding system in accordance with the presentinvention,

FIG. 6 illustrates the layer deposition step of FIG. 4 in more detail;

FIG. 7 illustrates the mixing step of FIG. 4 in more detail;

FIG. 8 illustrates the mold deposition step of FIG. 4 in more detail;

FIG. 9 illustrates the consolidation step of in more detail; and

FIG. 10 illustrates the follow-on heating and densification step of FIG.4 in more detail.

DETAILED DESCRIPTION OF THE INVENTION

The method and apparatus in accordance with the preferred embodimentenables the production of fiber-reinforced composite parts suitable foruse in manufacturing various components and high-friction applicationssuch as automobile, truck, and aircraft brakes. By combining fibrousmaterials with a binder material in a single apparatus, afiber-reinforced composite part with improved friction and wearperformance can be produced in fewer processing steps as compared to thecurrent techniques of the related art used to fabricate fiber-reinforcedcomposite materials, thereby providing increased reliability and reducedprocess cycle times. Additionally, the preferred embodiment allows formore complete control over defibrillation of carbon fibers so as toobtain a sufficient balance between strength/wear properties withadequate dispersion of mixed carbon fiber and matrix resin materials, ascompared to other manufacturing processes such as using a liquid slurry,for example.

FIG. 2 illustrates a schematic diagram of the equipment used inaccordance with the preferred embodiment. Referring to FIG. 2, thefiber-reinforced composite apparatus 200 includes a series of feeders210, 220, and 230, and a constituent transport arrangement, preferably aconveyer belt 205, which is situated below the feeders and adjacentlymounted to a first inlet 241 of a material handling fan 240. An outlet242 of the material handling fan 240 connects to inlet 249 of a cyclonedust collector 260 via line 245. A return air fan 250 takes a suctionoff the cyclone dust collector 260 at point 251. Additionally, thereturn air fan 250 includes an outlet 252 which is connected to a secondinlet 243 of material handling fan 240 via a line 255. The cyclone dustcollector 260 is arranged above a mold 270 that rests on a rotationaldevice 271. Further, fiber-reinforced composite apparatus 200 includes adust filter fan 280 that takes a suction from mold 270 at 275.

Feeder 210 may feed reinforcing fibers between about 0.5-1.5 inches(about 1.3-3.8 cm) in length at a first predetermined rate. Preferably,feeder 210 feeds 1-inch (2.54 cm) fibers (hereinafter “reinforcingfiber”); however, reinforcing fibers longer than 1.5 inches (3.8 cm) maybe used. Feeder 220 may feed milled and short fibers between about 100μm and ½″ (1.27 cm) in length, and preferably feeds 100 μm (0.1 mm)length fiber (hereinafter “milled fiber”) at a second predeterminedrate. The milled fiber acts as a “filler” fiber to fill in gaps betweenthe longer reinforcing fibers. Feeder 230 can be a resin feeder whichfeeds a resin binder material at a third predetermined rate.Alternatively, the fibrous materials from feeders 210 and 220 can be thesame size (for example, equal length fibers up to about 1.5 inches (3.8cm) in length). It is advantageous to use a mixture of longer andshorter fibers to obtain better friction and wear properties while stillmaintaining adequate strength in the finished component. The longerfibers provide the strength, while the shorter fibers fill in gapsbetween the longer fibers and the matrix material to help increase thefinal density of the intermediate-formed part/preform, and/or of thefinal composite part.

The chopped reinforcing and milled fibrous materials can bepolyacrylonitrile (PAN) based carbon fibers, preferably to be used forfabrication of carbon-carbon composite parts. However, glass fibrousmaterial or other reinforcing fibrous material such as metal fibers andsynthetic fibers, for example may be used, depending on the resultantcomposite part to be fabricated. The binder material can be ahigh-carbon yielding mesophase pitch resin matrix (i.e., in powderedform; however, phenolic resins and other thermoplastic or thermosettingresin materials in powdered form may be used as the binder material,depending on the resultant composite part to be fabricated.

The fibrous chop and resin binder fed from feeders 210, 220, and 230 aredeposited onto a belt conveyor 205 as a series of continuous, stackedlayers. This provides for a semi-continous process whereby the feederscontain a sufficient amount of materials to produce many compositeparts. The stacked layers travel along belt conveyor 205 to be dispensedinto a material handling fan 240. Material handling fan 240 mixes thefibrous and binder materials, while partially or fully defibrillatingthe chopped fiber materials from feeders 210 and 220. Alternatively, thefibrous chop and resin from the feeders may be fed directly into thematerial handling fan without a belt conveyer.

Material handling fan 240 further provides a volume of air flow toconvey the “mixed materials” via a line 245 to cyclone dust collector260. The cyclone dust collector 260 receives the air-entrained mixedmaterials and separates the solid particles of the materials from theair used to convey them. Return air fan 250 takes a suction of cyclonedust collector 260 to circulate the bulk of the air volume coming fromline 245 back to the material handling fan 240 via line 255, allowingthe remaining mixed materials to exit the bottom of the cyclone dustcollector 260 into mold 270. Dust filter fan 280 removes any residualdust created by the deposition of the mixed materials into the mold 270,and deposits dust particles into dust collector 285. To further ensureuniform deposition of the mixed materials from cyclone dust collector260 into mold 270, the mold can be arranged on a rotation device 271.

FIG. 3 illustrates a rotation device 271 to rotate mold 270 inaccordance with the preferred embodiment of the present invention.Rotation device 271 includes a turntable 272 mounted upon a support 274and connected to an electric motor 276 by a rotating spindle 273.Support 274 (along with turntable 272 and electric motor 276) can bejogged back and forth via air cylinders 277, and rests on a linearactuator 278. The entire assembly is supported by a table lift 279.

Turntable 272 and the combination of the air cylinders 277 and linearactuator 278 provide rotational and linear motion for mold 270 duringthe deposition process. In operation, turntable 272 is powered byelectric motor 276 via the spindle 273 to rotate the mold.Simultaneously with this rotation, mold 270 may be reciprocated in a +Xand −X direction for the duration of the deposition process by aircylinders 277, the cylinders essentially jogging the support 274supporting the turntable 272. The mold 270 is aligned to the outlet ofthe cyclone dust collector 260 such that it can be moved up to four (4)inches to either side of the centerline of the cyclone dust collector260 by adjusting linear actuator 278 (for example, the linear actuator“distance” can be set at positions such as −1.0″ (−2.54 cm) or +2.5″(+6.35 cm) from the centerline of the cyclone dust collector 260). Thejogging action imparted by air cylinders 277, together with the rotationimparted by turntable 272, ensures that the mixed material falling fromthe bottom of the cyclone dust collector 260 is uniformly dispersed inthe mold 270 as the mold 270 fills to a desired level, in preparationfor a subsequent consolidation step to be discussed later below.

FIG. 4 illustrates a process by which fibrous material and bindermaterials are combined to manufacture a fiber-reinforced composite partin accordance with the preferred embodiment. All parameters foroperation are initialized prior to operating the fiber-reinforcedcomposite apparatus 200 (Step S1). This includes determining the ratesat which the fibrous and binder materials will be gravimetrically fedfrom feeders 210, 220, and 230, respectively, onto conveyor belt 205.These rates are determined by a programmed processor (not depicted)running a software application, and are based on the desired ratios ofthese materials in the final formed fiber-reinforced composite part.Additionally, fan speeds are pre-set for each of the material handlingfan 240, return fan 250, and dust filter fan 280, and preferably do notchange throughout the entire manufacturing operation. Further, the beltconveyor speed for belt conveyor 205 and the turntable rotational speedand linear actuator distance for rotation device 271 are set, andpreferably do not change throughout the entire manufacturing operation.

FIG. 5 illustrates a feeding system in accordance with the presentinvention. Once the predetermined ratios are set, the gravimetricalfeeding of the chopped fiber and resin binder material is controlled bya feeding system 290. For example, as illustrated in FIG. 5, the feedingsystem 290 comprises the individual feeders 210, 220 and 230, a commonfeeder controller 235 and a set of load cells 211, 221 and 231 for eachfeeder. Each feeder has an electric motor 213, 223, 233 which drives acorresponding feeding mechanism or feed screw 212, 222 and 232 (such asan auger or roller with pins) to propel fibrous material from a storagehopper to a desired location (i.e., the belt conveyor 205). Therespective motors are driven by an electrical signal received via inputlines 236 by feeder controller 235, the signal ranging from 0-100% motorspeed.

As shown in FIG. 5, each feeder 210, 220 and 230 rests on acorresponding sensitive load cell 211, 221 and 231. These load cellsmeasure the weight of the feeder in small time increments (several timesper second) and sends a signal to feeder controller 235 via one of theinput lines 236 as the feeder is operating in the gravimetric mode. Thefeeder controller 235 calculates a feed rate over several of these timeincrements, and adaptively adjusts the motor speed of the feeder tocompensate by sending a signal via output lines 237 to the respectivemotors 213, 223 and 233. Thus, the average feed rate required to obtainthe desired ratio can be achieved over the operating period to conveyand mix materials for the resultant preform. Although in the preferredembodiment, a single feeder controller 235 preferably monitors allfeeders simultaneously during operation, each feeder can have its ownindividual feeder controller.

Once all parameters have been initialized, the operation proceeds withsequential deposition of chopped fibrous materials and resin bindermaterial onto conveyor belt 205 (Step S2). The layers are then mixed ina mixing step by material handling fan 240 (Step S3) and conveyed in anair volume to cyclone dust collector 260. There, the mixture of choppedfibrous materials and resin binder is separated from the air volume anddeposited into the rotating mold 270 (Step S4). Once the mold is filledto a desired level, a drag chain conveyor (not shown in FIG. 2 butsimilar to belt 205) is provided to transport the constrained mold ofmixed material to be consolidated. This provides a semi-continousprocess of part fabrication, since the feeders contain sufficientmaterial to make many individual parts. Thus, when one “filled” mold isconveyed away from underneath cyclone dust collector 260, another“empty” mold moves in and the filling cycle is repeated.

Once a mold 270 is filled to a desired level and removed from underneaththe cyclone dust collector 260, a consolidation process is performed byheating for in-situ impregnation of the fibrous material with the nowsoftened binder resin, and subsequently compacting the ingredients inmold 270 to obtain an intermediate fiber-reinforced composite part of adesired shape (Step S5). Thereafter, the intermediate composite part orpreform is ejected from the mold and subjected to follow-on heating anddensification treatments so as to obtain a final, fully-densifiedcomposite part (Step S6).

FIGS. 6-10 illustrate the steps of FIG. 4 in more detail. In FIG. 6,Steps S11-S14 correspond to Step S2 of FIG. 4. In FIG. 7, Steps S15-S17correspond to Step S3 of FIG. 4. In FIG. 8, Steps S18-S20 correspond toStep S4 of FIG. 4. In FIG. 9, Steps S21 and S22 correspond to Step S5 inthe process outlined in FIG. 4; and in FIG. 10, Steps S23-S28 correspondto Step S6 of FIG. 4.

Referring to FIG. 6, once all parameters have been initialized(completion of Step S1 in FIG. 4), the operation begins with the firstfeeder 210 gravimetrically depositing the reinforcing fibers at a firstpredetermined rate onto belt conveyor 205 (Step S11). The milled fibersand resin binder material from feeders 220 and 230 each have a staggeredstart such that the milled fiber chop and resin binder materials aresuccessively and gravimetrically deposited on top of the reinforcingfiber chop as the conveyor belt 205 passes underneath (Steps S12-S13).This forms a continuous tri-layer of materials on conveyor belt 205,which is subsequently dispensed into a material handling fan 240 (StepS14).

Referring to FIG. 7, the mixing step S3 carried out by material handlingfan 240 has several purposes: it provides the air flow which will conveythe combination of fibrous chop and resin binder material to the mold270. More importantly, it mixes together the layered materials (StepS15) while simultaneously defibrillating the reinforcing and milledfibrous chop materials into smaller fiber strands (Steps S16). Thedefibrillation step further breaks up the reinforcing fibers and milledfibers into smaller strands to promote even better mixing with the resinbinder material in material handling fan 240.

The use of material handling fan 240 allows control over the amount ofdesired defibrillation. Particularly, and unlike conventional liquidslurry processes for example, where defibrillation is complete inbreaking up a fiber tow into individual filaments, material handling fan240 allows for a wide range of defibrillation, breaking up the choppedfibrous material into smaller filament bundles ranging from hundreds offilaments to almost 10,000 filaments, thereby preserving strength whileproviding improved wear properties for the resultant finished compositepart. After mixing and defibrillation, the “mixed materials” areconveyed via line 245 to a cyclone dust collector 260 (Step S17).

Referring to FIG. 8, the cyclone dust collector 260 acts as a separator,in conjunction with a return air fan 250. Specifically, the “fluid”entering cyclone dust collector 260 is a mix of the defibrillatedfibrous chopped materials and resin binder materials entrained in a bulkvolume of air. The return air fan 250 acts as a vacuum to circulate thebulk of this air volume back to the material handling fan 240 via a line255. This air removal process allows the mixed materials to gently exitthe bottom of the cyclone dust collector 260 so that they are depositedinto the rotating mold 270 (Step S18).

To further promote uniform dispersion of the mixed materials in to themold 270, the mold is rotated during deposition by turntable 272 (StepS19). As the mold fills with the mixed materials, a dust filter fan 285simultaneously creates a suction on mold 270 that removes any entraineddust that is present when the mixed materials fill the mold 270 (StepS20).

Referring to FIG. 9, once the mold 270 is filled to a desired level, itis placed in an oven and heated to a temperature sufficient to softenand/or melt the resin binder material, preferably at about 300° C. and 1ATM (Step S21). After heating is completed, the mixed material iscompacted using a suitable method such as a hydraulic press, forexample, to impregnate the fiber tows and to obtain the desired finalshape of the intermediate composite part/preform (Step 22).

Referring to FIG. 10, the preform is cooled in the mold 270 until theresin binder material solidifies, and is then ejected from the mold 270.(Step S23). The preform then undergoes oxygen stabilization (Step S24)whereby it is heated in circulating air (preferably about 170° C.) foran extended period. Alternatively, this step could be performed in acyclic pressure device (sometimes called an iron lung), by thermallyshocking the preform to develop cracks, or by subjecting the preform toa high pressure oxygen treatment at about 40 psi. Following oxygenstabilization, the preform is subjected to carbonization, where it isslowly heated (preferably between 1°/min to 1°/hr) to about 600-900° C.in nitrogen at atmospheric pressure (Step S25). Following carbonization,the preform undergoes a chemical vapor deposition (CVD)/chemical vaporinfiltration (CVI) process for up to about 600 hours to achieve fulldensity (Step S26). CVD/CVI includes approximately 50-200 hours ofCVD/CVI infiltration followed by at least 400 hours or more of CVD/CVIcycles, or densification can be performed by resin transfer molding(RTM) cycles, to fully densify the preform. A final heat treat isperformed in a standard temperature range of 1600-2200° C. thereafter toobtain a near final (machining is also typically required)fiber-reinforced composite part such as a carbon-carbon compositeaircraft brake disc (Step S27).

EXAMPLE

Several test parts were fabricated using the above method and apparatus,specifically nine (9) stator and six (6) rotor-size parts for 767aircraft made by the BOEING Corporation. For a stator, 3.976 pounds(1807 g) of 1-inch (2.54 cm) chop length carbon fiber (grade X9755) and1.454 pounds (661 g) of milled carbon fiber (grade 341, each grade offibers marketed by FORTAFIL), and 7.176 pounds (3262 g) of AR mesophasepitch resin (pellets ground into powder) marketed by the MITSUBISHICorporation were dispensed onto a belt conveyer over approximately athirteen (13) minute period (a total of 12.606 pounds or 5723 g of“mixed material” was deposited in the mold over the time period to forma preform). The material handling fan was operating at 80% of themaximum motor speed, the return air fan at 37% of maximum motor speedand dust collector fan at 60% of maximum motor speed. The mold waslocated at a 2.5 inch (6.35 cm) linear position from the centerline ofthe cyclone dust collector and was turning 6 rpm during deposition.

For this example, the stator part was built up in two equal batches, dueonly to the current limitation of the 1-inch chopped fiber feeder'shopper capacity. After the fibrous and binder materials were mixed anddispensed in the mold, the mold was placed into an air circulating ovenand heated to a temperature of 315° C. for four hours. After heating,the preform was compacted with 30 tons of force until mechanical stopswere met. The preform thickness was maintained at 1.405″ (3.569 cm)until cool, and then was removed from the mold. The density of the 5490g weight preform was measured at 1.35 g/ cc.

Therefore the method and apparatus in accordance with the preferredembodiment enables the production of fiber-reinforced composite partssuitable for use in manufacturing various high-friction components forapplications such as automobile, truck, and aircraft brakes. The densityof the envisioned composite parts are between 1.2 and 1.5 g/cc. Bycombining low-cost chopped PAN-based carbon fibers with a high carbonyielding mesophase pitch matrix resin, a carbon/carbon compositematerial with improved friction and wear performance can be produced infewer processing steps as compared to current techniques used tofabricate fiber-reinforced composite materials, thereby providingincreased reliability and reduced process cycle times. Such frictionmaterials would typically have a density of at least 1.7 g/cc.

The invention being thus described, it will be obvious that the same maybe varied in many ways. For example, the constituent transportarrangement below feeders 210, 220 and 230 of FIG. 2 may be a pluralityof belt conveyors, each feeder having their own designated belt conveyerto transport the respective materials to a common mixing point. Inanother embodiment, a fourth feeder may be added to the apparatus inFIG. 2 to deposit other performance modifying additives which might benecessary in forming the resultant composite part. These additives caninclude materials such as metals, ceramic particles, graphite, cokes,curing agents, mica, carbon oxidation inhibitors, glass or polymerfilms, or any other agents or materials which improve friction and wearcharacteristics of a composite part and/or to further strengthen thefibrous/binder materials used to fabricate the composite part.Alternatively, these additives may be mixed in with the resin bindermaterial at feeder 230 to conserve space.

Additionally, in lieu of or in addition to performing oxygenstabilization (Step 24) of the intermediate part (FIG. 9), a supportfixture may be utilized during carbonization (Step S25) to preventbloating and maintain part shape. Further regarding FIG. 9, an optionalheat treat (HTT—High Temperature Treatment) may be performed betweencarbonization (Step S25) and CVD/CVI (Step S26), heating the preform atabout 1°/min to about 1800° C. Such variations are not to be regarded asa departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art, areintended to be included within the scope of the following claims.

1. A rotation device adapted for use in forming fiber-reinforcedcomposite parts, said rotation device comprising: a turntable forrotating a mold thereon; and an actuator for supporting said turntable,and for providing reciprocating motion to said mold, wherein saidturntable and actuator simultaneously rotate and reciprocate said moldduring a deposition of materials therein to provide improveddensification of the final formed composite part.
 2. The rotation deviceof claim 1, wherein said actuator is a linear actuator.
 3. The rotationdevice of claim 2, further comprising air cylinders for reciprocatingsaid mold in a +X and −X direction.
 4. A method of improvingdensification of a formed composite part employing a rotation deviceadapted for use in forming fiber-reinforced composite parts, said methodcomprising the steps of: rotating a mold on a turntable; and providingreciprocating motion to said mold with an actuator for supporting saidturntable, whereby said turntable and actuator simultaneously rotate andreciprocate said mold during a deposition of materials therein toprovide improved densification of the final formed composite part. 5.The method of claim 4, wherein said materials are mixed fibrous andbinder materials and wherein said simultaneous rotation andreciprocation provide substantially uniform dispersion of said fibrousand binder materials.
 6. The method of claim 4, wherein said actuator isa linear actuator and wherein said rotation device further comprises aircylinders for reciprocating said mold in a +X and −X direction.
 7. Themethod of claim 4, further comprising the step of: adjusting said linearactuator to move said mold up to four inches to a side of a centerlineof a cyclone dust collector.